Beam type of electron discharge tubes



April 1950 R. R. SYRDAL 2,505,261

BEAM TYPE 0F ELECTRON DISCHARGE TUBES Filed Aug. 29, 1947 3 Sheets-Sheet 1 55 13) W 43 attorney April 25, 1950 R. R. SYRDAL BEAM TYPE OF ELECTRON DISCHARGE TUBES s Sheets-Sheet 3 Filed Aug. 29, 1947 FFCE BEAM TYPE OF ELECTRON DISCHARGE TUBES Richard R. Syrdal, St. Louis Park, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application August 29, 1947, Serial No. 771,265

9 Claims. (01. 250-162) 1 2 The present invention relates to a beam type reference may be made to the following drawof electron discharge device and more particuings of which: larly to cathode ray tubes. It has been proposed Figure 1 is a view in elevation of a cathode ray to provide such devices with a plurality of target tube partly cut away embodying the invention;

plates and means for selectively deflecting the Figure 2 is an upper end view of the tube shown beam to cause engagement with one or more in Figure 1;

of said plates. It is an object of this invention Figure 3 is a cross-sectional view taken along to provide an improved device of this type. line 3--3 of Figure 1 in the direction of the ar- Another object of the invention is to provide rows and showing the target plates;

such an improved electron discharge device in Figure 4 is a partial fragmentary section of which substantially all of a high efiiciency elec- Figure 1 on an increased scale and showing one tron beam strikes at least one of a plurality of form of the invention;

coplanar target plates. Figure 5 is an elevation view of the target plates Another object of the invention is to provide shown partly in section;

an improved electron discharge device with a Figure 6 is a vertical sectional view in elevaplurality of target plates that are coplanar and tion of one form of electrode supporting insulatyet overlapping so that substantially all of a high ing member used in the form of the invention eiiiciency electron beam impinges at least one of shown in Figure 4;

the target plates. Figure 7 is a fragmentary section of the tube Another object of the invention is to provide and shows a second modification of the invention; such an improved electron discharge device uti- Figure 8 is a longitudinal sectional view of the lizing an insulating member having broad surelectrode supporting insulating member used in faces for rigidly engaging a plurality of electrodes the second modification of the invention as seen and firmly supporting them in proper spaced rein Figure 7; lation. Figure 9 is a bottom view of the electrode sup- Yet another object is to provide such an elecporting insulating member shown in the second tron discharge device in which an insulating memmodification of the invention as seen in Figure '7; her for supporting certain of the electrodes is Figure 10 is a cross-sectional view along line supported by a novel arrangement facilitating Ill-49 of Figure 4 in the direction of the arrows ready assembly of the device and accurate posiand showing the shape of the anode electrodes tioning of the electrodes. used;

Still another object is to provide such an elec- Figure 11 is a diagrammatic drawing of the tron discharge device sufliciently lightweight and cathode ray tube showing the voltages placed on compact that the entire electrode structure may the various electrodes; be supported entirely by a small number of in- Figure 12 is a graph showing the comparison sulating po ts, between the cathode current and target current Another object is to provide such an electron for changing grid voltage and the plate current discharge device in which potentials to various to cathode current ratio;

centering electrodes used are placed on the elec- Figure 13 is a diagram showing the shape of trodes by leads passing through specially pro- 40 the electron beam;

vided apertures in the insu ating posts used to Figure 14 is a cross-sectional view along line support the electrodes. liil4 in the direction of the arrows in Figure 4 In accomplishing the above objects, I provide showing the shapes of the centering electrodes the target plates with beveled edges so that the and the contacts to the aquadag from the last target plates may be coplanar even though overanode electrode; and

lapping. I also provide the electrode supporting Figure 15 is a side view of the control electrode insulating member with a ridge having surfaces used in Figure 7.

engaging a portion of the electrodes being sup- The electron discharge device is vertical and ported. The insulating member is mounted becomprises broadly an envelope containing an tween an electrode and a washer, both telescoped electron gun comprising means for emitting, diwithin and secured to a metal sleeve. I also emrecting, and focusing an electron beam along an ploy a number of novel features, the details of axis at the upper end, the leads to which pass which will be apparent from the following dethrough the envelope at the end adjacent to the scription. gun, and a plurality of mutually insulated target For a further understanding of the invention plates at the lower end which are situated in the 3 path of a beam emitted by the gun, the leads to said target plates passing through the envelope at the end adjacent to the plates.

Referring now to the drawings, the cathode ray tube in Figure 1 comprises an envelope having a coating of aquadag 2| over a major portion of the insideof the envelope. Inside the envelope and spaced at opposite ends are the electron gun 22 containing a plurality of electrodes and insulating support means therefor, and the;

target plate assembly 23 containing a plurality of target plates and insulating support means therefor, with the above mentioned aquadag extending from that portion of the. envelope near the middle of the electron gun down toward. the: target plates.

For a further, more detailed understandingv of the electron gun, reference is made to Figure 4. In the electron gun herein shown there are an electron emitting member or cathode 2 an ordinary. coiled wire heater element 28, a control electrode or grid 25, four anode electrodes: 2?, 36, 3|, 32", two springv members 33-, and two pairs of centering; electrodes 34; 35 and 3t, 39; These elec-- trodes; are symmetrical about an axis. The cathode 24 is tubular in shape and has a spherically concave-electron emissive surface 25. The heater element 28 is fittedinto'the tubular portionof thecathode. The grid 26 has a conical surface 42- which is concave away from the cathode; The

first anode electrode-21 has a spherical surface: concave away from the cathode; The remaining.

three anode electrodes 30, 3t and 32 have flat surfaces. The two spring members S's-make c0ntacta between anode electrode 32- and the aquadag H. The entire assembly can be said'to be the means for emitting, directing, and. focusing an cussed shortly. The'bottom surface of ridge 4'9 is' beveled to form aconcave conicalsurface 43.

extending outwardly away from the center.

. The-electron emissive electrode or cathode 24, containing a collar 36 which is. formed as part of the cathode, is inserted upwardlmwith the emissive surface facing down, through the central aperture 29 in the insulating member 31 until the collar 38: rests firmly against the lower surface 33 of the insulatingm'emberp A washer 49' is clamped-firmly, as by spot welding, around the cathode on the opposite side of the insulating member from the collar 36 to hold the cathode firmly with respect to the insulating member.

A;cylin'drical flange 8d, formed integral with the control electrode 26 and making anacute angle with the surface of the electrode, is firmly fastened, as by spot welding, to a cylindricalimetal sleeve 3! at the lower end of thesleeve. As shown in Figure l the'control grid is fastened to the inner surface of the metal sleeve. The grid 26 base conical surface 42 in order to help obtain the focusing characteristics desired. for the proposed use of this cathode ray tube; The re-- duced portion 58 of the insulating member 31' is to-provide thenecessary space for the grid flange 84 fastened'to the metal: sleeve when the insulating member 37 is telescoped down into the metalsleeve 4: to such a depth that the conical surface 42 of the grid is positioned on the ridge against the beveled surface 43 of the insulating member as shown at a. The beveled surface of the insulating member has the same conical shape as has the grid. 26 toprovide: a' broad, smooth surface for accurate positioning of the grid in close proximity to the cathode which is held firmly by the insulating member 31. A flanged washer 45 is telescoped within the metal sleeve ti against the upper surface of the insulating member and is fastened, as by spot welding, to the inner surface of the metal sleeve to holdth'e 'washer firmly against the upper surface Figure 10-shows' a metal: sleeveiifi: holding the; flat anode. electrode 30. firmlywith respect to a.

plurality, shownin the-drawing as two, hollow. inlsulatingz-posts 46., preferably made of .a ceramic Here it can-beseen thattheisleeve iscircularainshape and-has twowings; These Wings material.

haveycircula-r portions which surround theinsulatingzposts' lfi.

other along the axis-of the electron beam" due to the. metal sleeves being clamped firmly tothe:

posts whichv may be. considered a supporting means; The electrode 30, is fastened to its metal sleeve. 59; as'by spot welding, justasiare the other electrodes to their respective sleeves.-

Centering electrodes'sd", EE'and'BB; Bilare fastened to the: insulating postsl lfi' toward the bot tom: end-:of the posts.- Two heavy leads: 47 and 50 coming from the upper end of the envelope are inserted: through apertures provided in the insulatin posts it to hold the insulating posts;

and thus the electron gun; in. proper alignment within thertube;

supportedentirelyr'by means of: these. two 1115119 lating posts: mounted; on.- the: twov leads.

trode 35: andtlead 59 is; connected with centering electrode 33;.for reasonsxsoorrto-be described.

Connected',.as; by'riveting, to the fourth: anode 32" are two bowedv spring members: 33, shown". slightly offset in Figure which mak'e' contactn to the metal sleeve M to make? electrical con-- Pin 5k is connected to the' first andv third anode electrodes 2? and- 31 throughthe metal sleeves hold- Pin 55. is connectedto the nection with. the-;-control electrode 26'..

ing the electrodes.- fourth anode: electrode 32 through: itsmetal sleeve and from there to centering electrodesil and 39 and: to tlie aquadagjl; bymeans of the The wings'are crimped tofasten the metal sleeves firmly to the: insulating posts.. Thec'eramic posts it-align the various electrodes; in proper spaced relationship with respect'to each-v Due to the small size. of thetube:and" its components th'e electron gun can be In addi-- tion, lead 61 is connected: with: centering elec- Pins: 5t and 52' are connected v spring members 33. Pin 66 is connected to the second anode electrode 30 through the metal sleeve holding it.

The construction of the target plates 23 at the opposite end of the tube from the electron gun can be more clearly seen in Figures 3 and 5. The target plates 80, BI, 82, and 83 are shown to be mutually insulated and to have two converging, rectilinear beveled edges 65 which permit overlapping while at the same time enabling them to remain coplanar. The beveled edges of each plate form an angle equal to the angle formed by the beveled edges of each of the other plates. The edges are all beveled in the same direction and, as seen in Figure 3 looking down from above, the beveled edges extend radially from the center of the plate assembly through which the axis of the electron beam extends with each plate overlapping the plate counterclockwise to it. These target plates are fastened, as by riveting, as shown in Figure 5, to an insulating member 70 to hold them in their coplanar overlapping relationship. Insulating member 70 has apertures to permit leads ll passing through the adjacent end of the tube to make electrical connection with the plates 83, 8|, 82 and 83.

Figure 13 shows the formation of the beam due to the voltages placed on the various electrodes. Due to the shapes of the cathode and grid and the potential placed on the grid the beam leaves the cathode at a fairly high rate of convergence which continues until the aperture of the first anode electrode is reached. The lens system caused by the shapes of the anodes and the potentials impressed thereon decrease this rate of convergence. At point b the repelling effect of the electrons in the beam toward each other have finally equalized the convergence effect placed upon them by the lens system. Be-

yond point b the repelling effect becomes greater and the beam diverges until it hits the target plate assembly. It is desired that the cross-section of the beam striking the target plate be of such size that, when properly deflected, it can impinge on only one plate, but that a slight movement to either side will cause a portion of the beam to impinge one of the adjacent plates. This eliminates one possibility of havin a "dead spot which would occur if the beam could move a bit toward one side of a plate and yet still remain entirely on that target plate. A second possibility of having a dead spot is also eliminated by the overlapping target plates in that there are no gaps between the plates to receive a portion of the beam when it moves off one of the plates. Because there are no dead spots the sensitivity of the tube is greatly increased. The beam shown in Figure 13 is striking all of the target plates equally.

A set of voltages which have been found to work satisfactorily on the electrodes in this tube to give the desired shape of the electron beam as shown in Figure 13 can be seen in diagrammatic form in Figure 11. In this figure, the cathode 2 is shown to be at zero potential with the voltages on the remaining electrodes taken with respect to the cathode voltage. The heater 28 is shown at zero potential with an A. C. voltage of 6.3 volts applied to the heater winding. The control electrode 26 is shown at volts with an A. C. modulating voltage of 6.3 volts applied. The first anode electrode 2'! and the third anode electrode 3i are at +310 volts potential. The second anode electrode 30 is at +75 volts potential. electrode .32, the centering electrodes 34 and 39 The fourth anode and the aquadag 2| are at +240 volts potential. The other centering electrodes 35 and 38 are connected to variable taps to obtain a proper setting of potential to center the electron stream when there is no deflecting force. When these voltages for the centering electrodes 35 and 38 have been obtained the connections to the potentiometer are soldered fast to hold the settings at these positions. The target plates 80, BI, 82 and 83 are at a potential of +310 volts.

The four target plates are connected to two transformers l2 and 13. Target plates 8! and 83 are connected to opposite ends of the primary of transformer 72 while target plates 88 and 82 are connected to opposite ends of the primary of transformer 13. The secondaries of the transformers l2 and 13 are connected to any applicable si nal receiving device. When there is no defiecting force the electron beam strikes squarely in the center of the target plate assembly, each target plate receiving an equal portion of the beam. When a force, such as the earths magnetic field, deflects the beam, for example to the right, target plate 8! will receive an increased number of electrons while the number of electrons impinging plate 83 will decrease and thus cause a difference of potential at the opposite ends of the primary of transformer 12 to cause a current flow. Because the beam is modulated by the control grid the voltage across the primary and the current flow through the primary of the transformer is A. C. and thus induces a voltage in the transformer secondary. The four plates correspond to the four directions; north, south, east and west.

Transformer 72 may be considered as the transformer sending out .asignal for an east or west deflection of the beam while transformer 13 may be considered as the transformer sending out a signal for north or south deflection. Because of the overlapping target plates the only portion of the beam which is lost, that is, which does not strike any of the target plates, is that portion of the beam which strikes the very center of the target plate assembly where the four target plates come together. Because of the very small size of this hole and its position with respect to the tar-.

with certain small exceptions are the same as those shown in Figure 4. The changes come inv the lengths of the fianges of the control electrode and first anode electrode and the pins on the fianges of the two above mentioned electrodes. The second, third and fourth anode electrodes and centering electrodes are all mounted on two ceramic posts just as is done in Figure 4. The spring members making electrical connection between the aquadag and the fourth anode electrode are the same as shown in Figure 4;. The connections from the pins passing through the end of the envelope are all the same as those in Figure l. The insulating member shown in Figure 7 supporting the cathode and grid also sup ports the first anode electrode. This insulating member es supports the cathode 24 in the same manner as does insulating member 31 in Figure 4. The cathode is bound to the insulating member by a collar formed on the cathode and a washer. This member 60 is provided with an annular ridge on its bottom surface to provide a plurality of; surfaces to engage the control elec-;

trode and ;j the: anode electrodeands-toeaid: innposie, tioning: and supporting them. inproper. spaced! relation toward eachother and with-respect to the cathode. The control electrode 1.3: is pOSi'. tioned onzthe inside surface;-o:.ridge.-6-3: on the insulating. member 513 and-'has'twmpins 56 which.

fit. into holes. 52. inthe; insulating. member. and

through which electrical connection can bamade.

This control electrode with. itSitWO :pinscan per-a. haps be better seen in Figure 15. 'Ifhe:;first.anode electrode 115' is positionedion the outer surface of ridge 63 and has'two .pins. 6?? which fitintoi-holes.

6i through which electrical connections. canbe made. The same pins make connection to. the

control electrode and first anode electrode inthis. modification of the invention as in. the other even, though the manner of makingthe: connectionis.

slightly different. With the exception of a cylindrical surface rather thania conical surface and its larger size the first anode electrode resembles closely the appearance of the control. electrode and target current Ip, ranging in the order of 0.5'

to 1.5. milliamperes, which-can be obtained with this tube using either modification. Figure 12 also-shows the. high: efficiency; targetv currenttocathode current ratio, of this tube. This efficiency over the level portionof the curve averages better than 95%, dropping offat a. grid voltage of less than 45Y and greater than- Thehigh target current is due. tothew-ide apertures used in the electrodes and to. the. superior 'lenssystem used. The efficiency drops oil at the low end because of the large negativegridvoltage. which,

tends to drive the electronsbackjto the cathode.

The dropping 01? ofthe efiiciency at the high endis due to the small negativevoltage on the grid which is unableto prevent thebeam'from spread-1 ing and as a. result aportion, which increases; with a positive incrcasein' gridvoltage; strikes;

the first anode electrode.

It will be seen from the above description that I have provided ahigh efficiencytube, the high. efficiency of which isdue to the beveled, overlapping target plates which cause all but a very. small? portion of the beam leaving the. electron gun to.-

impinge at least one of the plates and to the iiigenious gun structure which focuses and directs virtually the entire beam ofelectrons leaving the cathode along an axis toward the target plate assembly. It will also be seen thatdue to the small size of the tube the only supportmeans. necessary for the gun are the insulating posts and". the conductingleads passing therethrough, said leads serving the double purpose of positioningthe posts and putting a potential on various of" the centering electrodes.

Although specific examples of. the invention have been shown and described, it will be under-- stood, of course, that they arebut illustrative and that various modifications may be made therein without departing from the scope and spirit of' this invention as defined in the appended claims.

I claim:

1. An electron discharge device comprising means including'a plurality of-electrodes and ill-- caltsurfaceyof the insulating member to position.

said: second electrode in proper. relation to said firstselectrode; and, target means located in the. path of. said. electron beam. for impingement. thereby:

2...An electron discharge device comprising. a

pluralityof electrodes. directing an electron beam along an axis; an insulating member having; a centrally located. aperture for the insertion therein..ofa.first of said electrodes and a conical surfaceiextending outwardly'from said aperture; a,

sleevehaving fastened-thereto a second of said: electrodes. and telescoped about said insulating member such that said second electrode rests. against said conical-surface; a. washer telescoped within said sleeveand fastened thereto prevent-v ing longitudinal movement of the insulatingmember Within the sleeve; a plurality of insulating posts to which said sleeve and the remaining electrodes. are secured to. position the electrodes in. proper spaced relationship along said axis; and. target means located in thepath of said electron beam for impingement thereby.

3. A cathode ray tube comprising an envelope; an electron gun in said envelope having a plural.- ity of electrodes, including an electron emissive electrode, for emitting, directing, and focusing a converging electron beam along an axis, an insulating member having a centrally located aperture for the insertion therein of the electron emissive electrode. and further provided with an annular ridge havin two of its surfaces coaxial with the longitudinal axis of said centrally located aperture and a third surface beveled to form a conical surface concave away from the. aperture, a second of said electrodes being conical inshape and positioned on said insulating member: with said conical portion of the electrode resting. on the beveledsurface of said ridge. so. thatthe. ridgepositions the second electrode in close'proximity to the firstelectrode, and means including a. plurality of insulating posts and a metal sleeve enclosing said insulating member positioningv the insulating member and said elec.-. trodes with respect to the. remaining electrodes of-"said'gun along said axis; and target means,

. also in said envelope, located in the path of said electron beam for impingement thereby.

4..A.cathode ray tube comprising an envelope; anzele ctron gun .in. said envelope having a plurality of electrodes, including an electron emissive. electrode, for emitting, directing, and focusing a converging electron beam alone. an axis, an insulating member having a centrally located aperture for the insertion therein oi the elec-v tron emissivev electrode and further provided with an annular ridge having two of its surfaces coaxial with thelongitudinal axis of. said centrally located aperture. and a third surface beveledto form a conical surface concave away from. the aperture, a metal sleeve to which is fastened a second of said electrodes conical in shape, aflanged washer, and insulating posts, said insulating member being telescoped within said metal sleeve with said beveled surface against the conical portion of the second electrode and said washer being. telescoped within said sleeve and.

fastened thereto to prevent longitudinal movement of the insulating member said insulating posts supporting said sleeve and the remaining of said electrodes in proper spaced relation along said axis; and target means, also in said envelope, located in the path of said electron beam for impingement thereby.

5.- A cathode ray tube comprising an envelope having an aquadag coating over a large portion of its inner surface; an electron gun in said envelope having a plurality of electrodes, including an electron emissive electrode and a plurality of centering electrodes, for emitting, directing, and focusing a converging electron beam along an axis, an insulating member having a centrally located aperture for the insertion therein of the electron emissive electrode and further provided with an annular ridge having ,two of its surfaces coaxial with the longitudinal 'axis of said centrally located aperture and a third surface beveled to form a conical surface concave away from the aperture, a second of said electrodes being conical in shape, and positioned on said insulating member with the conical portion of said second electrode resting on the beveled surface of said ridge so that the ridge positions the second electrode in close proximity to the first electrode, and means including a plurality of insulating posts and a metal sleeve enclosing said insulating member positioning the insulating member and said electrodes with respect to the remaining electrodes of said gun along said axis, one of the remaining of said electrodes making contact with said aquadag to put the potential of said electrode on said aquadag, said insulating posts being hollow to permit passage of heavy wire leads therethrough to support said insulating posts and connected to various of said centering electrodes to put a potential thereon; a plurality of coplanar, mutually insulated target plates each having two converging, rectilinear beveled edges, said beveled edges of each plate forming an angle equal to the angle formed by the beveled edges on each of the other plates; and means mounting said plates in the path of said beam with said beveled edges in overlapping relationship so that substantially every portion of said beam impinges at least one of said target plates.

6. A cathode ray tube comprising an envelope; an electron gun in said envelope having a plurality of electrodes, including an electron emissive electrode, for emitting, directing, and focusing a converging electron beam along an axis, and an insulating member having a centrally located aperture for the insertion therein of the electron emissive electrode, said insulating member being further provided with an annular ridge having two of its surfaces coaxial with the longitudinal axis of said centrally located aperture and having an electrode engaging each of said surfaces positioning them relative to each other and to said electron emitting electrode, said electrodes being positioned with respect to the rest of the electron gun by said insulating member supported on leads through the end of the envelope, a plurality of said leads extending the length of the gun and supporting the remaining electrodes of said gun along said axis; and target means, also in said envelope, located in the path of said electron beam for impingement thereby.

7. A cathode ray tube comprising an envelope having an aquadag coating over a large portion of its inner surface; an electron gun in said envelope having a plurality of electrodes, including an electronemissive electrode and a plurality said centrally located aperture and having an electrode engaging each of said surfaces positioning them relative to each other and to said electron emitting electrode, said electrodes being positioned with respect to the rest of the electron gun by said insulating member supported on leads through the end of the envelope, a plurality of said leads extending the length of the gun and supporting the remaining electrodes of said gun along said axis, one of th remaining of said electrodes making contact with said aquadag to put the potential of said electrode on said aquadag, said leads extending the length of the gun being positioned within hollow insulating posts and connected to various of said centering electrodes to put a potential thereon; a plurality of coplanar, mutually insulated target plates each having two converging, rectilinear beveled edges, said beveled edges of each plate forming an angle equal to the angle formed by the beveled edges on each of the other plates; and means mounting said plates in the path of said beam with said beveled edges in overlapping relationship so that substantially every portion of said beam impinges at least one of said target plates.

8. A cathode ray tube comprising an envelope; an electron gun in said envelope having a plurality of electrodes, including an electron emissive electrode, for emitting, directing, and focusing a converging electron beam along an axis, and an insulating member having a centrally' located aperture for the insertion therein of the electron emissive electrode, said insulating member being further provided with an annular ridge having at least one of its surfaces coaxial with the longitudinal axis of said centrally located aperture and having an electrode engaging said surface positioning it relative to said electron emitting electrode, said electrodes being positioned with respect to the rest of the electron gun by said insulating member supported on leads through the end of the envelope, a plurality of said leads extending the length of the gun and supporting the remaining electrodes of said gun along said axis; and target means, also in said envelope, located in the path of said electron beam for impingement thereby.

9. A cathode ray tube comprising an envelope having an aquadag coating over a large portion of its inner surface; an electron gun in said envelope having a plurality of electrodes, including an electron emissive electrode and a plurality of centering electrodes, for emitting, directing, and focusing a converging electron beam along an axis, and an insulating member having a centrally located aperture for the insertion therein of the electron emissive electrode and further provided with an annular ridge having at least one of its surfaces coaxial with the longitudinal axis of said centrally located aperture and having an electrode engaging said surface positioning it relative to said electron emitting electrode, said electrodes being positioned with respect to the rest of the electron gun by said insulating member supported on leads through the end of the envelope, a plurality of said leads 11 extending the length of theigunuand supporting theiremaining .:electrodes .of saidrgun along said axis, one of theremainingof saidelectro'des makoingcontact withsaidaquadagsto put the vpotential-o'f said electrode on. said aquadag, said leads 7 extending thelength of thegun being positioned within hollow insulating ,posts and connected to various of said centering electrodes to put a ..potential thereon; .a plurality of coplanar, .mu-

tually insulated target plates \each'having two converging, rectilinear beveled edges, said bevoelededges ofeach plateformingoan angle equal .totheangle formedbyrthe beveled edges on each ..of the other plates; and means mounting said plates in the path of said beam withosaid beveled edges in overlapping relationship so that substantially every portion of said beamcimpinges .at leastone of saidtarget plates.

RICHARD "R. .SYRDAL.

112 REFERENCES :The:.-'fo1lowing:references-aareadf record in the file of this patent:

UNITED STATES PATENTS Number Na-me rDate 1,977,398 Morrison :Oct. '16, 1934 2,011,920 .'I',err y, -Aug. 20, .1935 2,093,8 7 6 NonArdenne .Sept. 21, .1937 2,163,233 Brown June 20,1939 2,184,821 Uhlmann Dec. 26,1939 2,185,807 .Gab.or.et a1 .Jan..,2, 1940 2,3025 11 iGoldsmith Nov.v .17, 1942 2,436,265 Rohlecet a1 Feb. 17, 19.48 2,440,889, Binneweg, Jr May 4,1948 2,443,916 Kelar .June -22, 19.48

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